The present invention relates to a method and an apparatus for forming, filling and sealing synthetic plastic bags containing most preferably liquid contents, although the present invention is applicable also to filling bags with powder and similar materials.
The fabrication of synthetic plastic bags filled with liquid has caused problems in the past because of the ready breakage of the seals thereof under the strains applied to the walls of the plastic bags. When the bags are placed one on top of the other where the buttommost bags must support the weight of the bags thereabove, or in those instances where the bags are dropped, the rupturing of the seals of the bags are not an uncommon occurrence. One of the reasons for the rupture of the bags is due to the difficulty of making secure heat seals between the confronting walls of the bags.
The plastic sheets from which plastic bags are made are generally formed by extruding the plastic material through a thin orifice. Bags are commonly formed from such extruded plastic material by wrapping the sheet around a mandrel or by placing two sheets in confronting relationship and heat sealing the confronting edges thereof. It is known that when the heat seals run in the direction in which the plastic material was extruded, the resulting seal is appreciably weaker than seals formed at right angles to the extrusion direction thereof. The avoidance of seals running in the direction of the extrusion of the plastic material is achieved by forming the bags from tubular plastics stock so the only seals which are formed extend transversely of the extrusion direction. In such case, filled sealed bags can be formed by severing a section thereof from the tubular stock of material involved, forming a seal at the bottom end thereof, filling the bag from the top thereof and then sealing the top of the bag. U.S. Pat. No. 3,492,775 to Rhine et al. and U.S. Pat. No. 3,760,558 to Kaminsky et al. show two examples of apparatus for forming, filling, and sealing individual bags formed on the end portion of an initially flattened tubular plastic stock. In the apparatus involved in these patents, rather complex mechanical means are located within the tubular stock pulled thereover for the purpose of separating the initially flattened walls of the plastic stock so it can receive a spout for filling the same, and also for isolating portions of the bag to be sealed from the material being injected into the same. Such mechanical means are relatively complex and expensive to manufacture and not readily useable when the bags are to be filled with liquid materials, and generally are not adaptable by adjustment to make bags of greatly different lengths. Also, because of the mode of operation of these prior bag forming, filling and sealing apparatus there were undersired limitations on the rate at which the bags could be formed, filled and sealed. In the case where liquid is the filling material, such material coating the mechanical means could drip upon portions of the stock to be sealed and prevent proper seal formation.
It is, accordingly, one of the objects of the present invention to provide a method and an apparatus for fabricating, filling and sealing individual plastic bags from the end portions of a strip or roll of flattened extruded tubular synthetic plastic material and which further is of much less complexity and greater reliability than the apparatus heretofore used for this purpose.
A related object of the invention is to provide apparatus for forming, filling and sealing plastic bags formed from the end portions of flattened tubular stock of synthetic plastic material which does not require the insertion of any apparatus into the tubular stock, except for one or more filling spouts. A related object of the invention is to provide a method and an apparatus as described which can be readily adapted to make bags of varying lengths and with secure seals in all cases.
Another object of the invention is to provide apparatus for forming, filling and sealing plastic bags formed from the end portions of flattened tubular stock of synthetic plastic material which can produce separate filled bags at a much higher rate than the prior art apparatus.